Sinning, as Jesus and the church say, is good. Turn or burn Christians.

[Greatest I am]

Just as before, it cannot be true that there is no harm, loss, or evil in cooperation...if there is lesser harm, loss or evil in cooperation - and even that claim is iffy.  

At any rate, if sin is somehow hereditary or intrinsic to human beings, then ofc a child could sin and be sinful as well.  You can hold to whatever beliefs you like about evil, competition, and cooperation - but sin isn't what you're talking about in that case.

What would you say is the thing that compels people to competition, instead of cooperation?  That thing, whatever that is for you, would be the kind of thing we're discussing when we consider the concept of sin.

You are still not showing the evil/sin of cooperation.

To your last.

We are all born the fittest of our line. We all want to rule, as the fittest of our line.

We cooperate until we see a time where we can show ourselves as the fittest. 

It becomes clearer if you look at other tribal animals. You see the cubs cooperating and playing, until the mating urge starts and then the play become fighting for the right to breed.

The young cub will bide his time cooperatively for the security of the group, until he thinks himself fit enough to take it over.

Regards
DL